Best to do engine cleaning with the cover up/off, but with engine running so you can back off if the water starts givings you misfires. With a high pressure car wash wand, with high pressure water should clean up zip-sip, get the area behind the power steering reservoir so that later you can check if the seepage there is from oil fills dripping down from the oil fill cap, or if you have seepage from a leaking o-ring on the power steering reservoir.

I, personally, wouldn't spray water on the engine unless I covered the alternator first.

Yes, I forgot to mention that though I don't cover the alternator, I don't douse it with H2O, I do rinse the alternator out. I have done this for all my Nissans, my E, the MLs, my Bimmer and even my VW and none of them have died yet. The Nissans, I can start right away with no issues. The Germans, I usually wait a while, but not tens of minutes. So far I have had no issues at all. The key is not to use high pressure because that may penetrate the seals on the plugs and that would result in issues.

Best to do engine cleaning with the cover up/off, but with engine running so you can back off if the water starts givings you misfires. With a high pressure car wash wand, with high pressure water should clean up zip-sip, get the area behind the power steering reservoir so that later you can check if the seepage there is from oil fills dripping down from the oil fill cap, or if you have seepage from a leaking o-ring on the power steering reservoir.

You may be right, but I have never done it with motor running - messy anyway. I usually do it with motor off and cold and not high pressure. The one time I tried HP on my E, I had problems - the cooling fan shorted out and stayed on until MB roadside advised me on what to do. I still say use some kind of non corrosive degreaser and, stay with low pressure and motor off.